Generally, a lubrication device of this kind is configured to be able to suck up the oil stored in the oil pan by means of an oil pump and to feed the sucked-up oil to members-to-be-lubricated (e.g., gears, cam shafts, cylinders, pistons, etc.) in the mechanism-to-be-lubricated. The lubrication device is configured to provide a lubricating action for the members-to-be-lubricated and such that the oil which has absorbed heat, such as frictional heat, from the members-to-be-lubricated returns into the oil pan from the mechanism-to-be-lubricated under the action of gravity.
A widely known structure for the oil pan is a so-called 2-chamber-type oil pan structure, which can accelerate the progress of a warming-up operation by means of accelerating an increase in temperature of the oil. The oil pan having the 2-chamber-type oil pan structure (hereinafter, referred to merely as the “2-chamber-type oil pan”) is configured such that the interior of the oil pan is divided into two chambers; namely, a main chamber (may be referred to as a first chamber) and a sub-chamber (may be referred to as a second chamber).
The lubrication device having the 2-chamber-type oil pan is configured to feed the oil contained in the main chamber to the mechanism-to-be-lubricated. The 2-chamber-type oil pan is configured to restrict the flow of the oil between the main chamber and the sub-chamber during a warming-up operation, in which the temperature of the oil (and the temperature of the members-to-be-lubricated) is low, and to cancel the restriction after completion of the warming-up operation when the temperature of the oil (and the temperature of the members-to-be-lubricated) has increased to an appropriate level.
The 2-chamber-type oil pan operates as follows. First, during the warming-up operation, the flow of the oil between the main chamber and the sub-chamber is restricted. This restricts the amount of the oil to be circulated between the mechanism-to-be-lubricated and the oil pan virtually to the amount of the oil stored in the main chamber. Therefore, the temperature of the oil contained in the main chamber (and the temperature of the members-to-be-lubricated) increases promptly, so that the progress of the warming-up operation can be accelerated.
After completion of the warming-up operation, the restriction is mitigated or canceled. This enables the oil stored in the sub-chamber to flow into the main chamber. Specifically, substantially the whole quantity of the oil contained in the oil pan can serve in circulation between the mechanism-to-be-lubricated and the oil pan. Therefore, in the mechanism-to-be-lubricated, the oil can carry out good lubrication and cooling.
Known examples of such the 2-chamber-type oil pan are described in Japanese Patent Application Laid-Open (kokai) No. 2003-222012 (Patent Document 1) and Japanese Patent Publication (kokoku) No. 5-43850 (Patent Document 2).
According to the configuration described in Japanese Patent Application Laid-Open (kokai) No. 2003-222012 (Patent Document 1), an oil pan separator is disposed in the inner space of the oil pan. The oil pan separator is configured and disposed to divide the inner space of the oil pan into two chambers; namely, the main chamber and the sub-chamber.
The main chamber is formed in such a manner as to open toward an engine block, which serves as the mechanism-to-be-lubricated. The main chamber is provided in a communicating relation with the engine block so as to be able to receive the oil that returns to the oil pan from the engine block. An oil strainer is disposed in a bottom region of the main chamber. The oil strainer is connected to the oil pump and has a suction port through which the oil residing in the main chamber is sucked up.
The oil pan separator has first communication holes and second communication holes for establishing communication between the main chamber and the sub-chamber. The first communication holes are located above the second communication holes, and each has a larger opening diameter than do the second communication holes. For example, several first communication holes are formed as circular through-holes each having a diameter of about 8 mm. A large number (10-odd to tens) of second communication holes are formed as circular through-holes each having a diameter of about 2 mm.
In the 2-chamber-type oil pan having the above configuration, a change in viscosity of the oil associated with a change in temperature of the oil controls the flow condition of the oil between the main chamber and the sub-chamber.
Specifically, during the warming-up operation, the oil which resides in a bottom region of the sub-chamber and which is low in temperature and high in viscosity encounters difficulty in passing through the second communication holes, which are small in opening diameter and are formed at a lower level. Even during the warming-up operation, the oil that resides in an upper region of the sub-chamber and is relatively high in temperature can readily flow into an upper region of the main chamber through the first communication holes, which are large in opening diameter and are formed at an upper level. Meanwhile, as the warming-up operation progresses, and thus the temperature of the oil in the sub-chamber rises, the oil can flow between the main chamber and the sub-chamber through the first communication holes and through the second communication holes.
According to the configuration described in Japanese Patent Publication (kokoku) No. 5-43850 (Patent Document 2), a partition that separates the main chamber and the sub-chamber from each other has a communication section. The communication section has a valve device that operates according to the temperature of the oil contained in the main chamber. The valve device has a thermostat valve, which is closed until the temperature of the oil rises to a high-temperature-side set temperature (e.g., about 60° C.) which is a relatively high temperature as a result of the warming-up operation and which opens when the temperature of the oil rises to the high-temperature-side set temperature or higher.